The Air doesn't have a touch bar and costs less money. It's also a perfectly good -- no, sorry: an excellent laptop for most applications, including development.

I suspect the 13" M1 Pro was probably just something to cater for those who were skeptical about a fanless laptop since no one really knew back then how well these machines would perform. Now that the M1s have been out for a while and no one seems to be complaining about the Air, they can drop the M1 Pro.